1. Field of the Invention
The present invention relates to a separately-excited inverter circuit and a liquid crystal television, and more particularly, to a separately-excited inverter circuit for converting the input DC voltage into the AC voltage by the separately excited switching circuit so as to be output, and a liquid crystal television with the separately-excited inverter circuit.
2. Description of the Related Art
Generally, a solder portion of a circuit substrate is likely to get into trouble owing to the contact failure caused by the oscillation during the transportation, the drop impact, loosening or peeling off as passage of time and the like. The use of the circuit substrate in the aforementioned state with the contact failure may cause the noise waveform in the signal transferred through the circuit. Especially in the secondary side of the inverter circuit where the high voltage signal is transferred therein, the contact failure may impose the undesirable effect.
Generally, in the known process for coping with the trouble in the circuit, the noise waveform generated in the circuit is detected by the transistor, the operational amplifier, and the comparator, and the detection result is input to the microcomputer for executing the program to perform the protective function. The aforementioned protective function is structured not to detect the noise waveform with the short time width for the purpose of preventing the malfunction. It is therefore difficult to detect the noise waveform momentarily caused by the contact failure.
The technology for detecting the trouble in the circuit is disclosed in Japanese Unexamined Patent Application Publication No. 2006-120515. The document discloses that in the full-bridge type separately-excited inverter circuit, the frequency signal generated between the full-bridge and the pressure-rising transformer is detected, and when the detected frequency signal deviates from the preliminarily stored reference frequency or from the reference frequency range, the power supply to the separately-excited inverter circuit is interrupted.
Japanese Unexamined Patent Application Publication No. 2002-313592 discloses that a plurality of avalanche diodes are connected in series in the section where the predetermined potential difference is expected to occur, and when the potential difference becomes higher than the predetermined value, the avalanche diode breaks to protect the circuit.
Each art disclosed in Japanese Unexamined Patent Application Publication Nos. 2006-120515 and 2002-313592 is not intended to protect the circuit by detecting the noise caused by the contact failure which may result in the trouble therein.